In the games

As the protagonist

Rosa is a young girl living in Aspertia City with her childhood friend Hugh. At the start of the game, she sets off with Hugh to collect her first Pokémon. They then go their separate ways and she starts her journey across the Unova region.

Rosa will then appear as the player's partner in the Battle Subway when choosing to ride the Multi-Train. Two of the following Pokémon are picked from the corresponding list, depending on what the player wants her to base her team on. If the player chooses "A balance between the two," Rosa's Pokémon are chosen from either list.

Quotes

In front of the Battle Subway

Before battle

"I heard that in Gear Station you can have Pokémon battles in the subway! So I came here to test my skills, and, what do you know… the Subway Bosses were here! Isn't that amazing? I mean, they're the strongest Trainers in Gear Station! And they said they'd battle if it's two on two! This is an a-MAZ-ing opportunity! Would you PLEASE battle with me?"

Yes: "Thanks! Oh! The name's Rosa! Let's become the best partners ever and surpass the Subway Bosses! So I'll have you challenge the Subway Bosses with me, then!"

After battle

"They were so tough, even when they were holding back for us! That's the Subway Bosses for you! I want to get even stronger and battle the Subway Bosses when they're giving it their all! Thanks, <player>! This is a token of my appreciation! Please take it!"

"When you have the Vs. Recorder, you can record your battles with your friends or battles on the Battle Subway!"

"<Player>! I had a really great time battling with you! I hope we can battle together again sometime! See you!"